Deep Levels and Hydrogen Evolution in Hydrogenated Amorphous Silicon

Two hydrogen-mediated models are applied to predicting the density of deep levels in hydrogenated amorphous silicon (a-Si:H) under variations in the material’s temperature and total hydrogen content. Both models depart from the assumption that hydrogen is bonded at two classes of sites, dangling bonds and weak bonds. The predictions of the two models for the temperature-dependence of the deep-level density are similar. The models differ in their treatment of the origins of the weak bonds; a model associating the weak bonds with the clustered phase of bonded hydrogen observed by nuclear magnetic resonance also appears to be in agreement with hydrogen evolution experiments.